I know this is kind of an old thread, but here's my two cents.
Blacklights don't work well on aquariums because usually, aquarium water is too dirty - it looks like you're illuminating chocolate milk. It will work in regular tap water, so maybe all you need to do is more water changes to dilute the dissolved organic compounds. But with 4 goldfish in a 55 gallon tank, the water is bound to never be crystal clear.
Zebra danios can't tolerate more than 65 degrees I don't believe, but fancy goldfish don't like it this cool either (unlike commons) so actually the temperature is compatible. They are likely to compete for any food at the top, but goldfish should get lots of food at the bottom too, such as algae wafers, fresh veggies and pellets, which are a lot more stable than flake. New Life Spectrum goldfish pellets are a great staple.
Some goldfish do eat smaller fish, but not all. I've had white clouds with my black moors for nearly 2 years now, and they're all still there.
The goldfish are over 3 years old now.
Blacklights don't work well on aquariums because usually, aquarium water is too dirty - it looks like you're illuminating chocolate milk. It will work in regular tap water, so maybe all you need to do is more water changes to dilute the dissolved organic compounds. But with 4 goldfish in a 55 gallon tank, the water is bound to never be crystal clear.
Zebra danios can't tolerate more than 65 degrees I don't believe, but fancy goldfish don't like it this cool either (unlike commons) so actually the temperature is compatible. They are likely to compete for any food at the top, but goldfish should get lots of food at the bottom too, such as algae wafers, fresh veggies and pellets, which are a lot more stable than flake. New Life Spectrum goldfish pellets are a great staple.
Some goldfish do eat smaller fish, but not all. I've had white clouds with my black moors for nearly 2 years now, and they're all still there.
The goldfish are over 3 years old now.